Are They Crying Wolf?

Cessna 421C
On the night of November 10, 2012, a twin-engine Cessna 421C broke up in flight near Shaver Lake, Calif. The private pilot and his father were killed. A post-crash fire consumed a lot of the wreckage. The airplane took off from Salinas Municipal Airport, Salinas, Calif. The father and son had been at a raceway's driving academy and were flying to Omaha, Neb.

According to the pilot's wife, they had strong headwinds going to California and wanted to take advantage of tailwinds by making the return flight that night, rather than stay in a hotel. The pilot planned to drop his father at Omaha and then fly home to Missouri the following day.

According to FAA recordings, the pilot was given an IFR clearance to Omaha and read it back correctly. After leveling at the cruise altitude of FL 270, the flight was cleared to a VOR, then direct to Omaha. The pilot acknowledged and, for the next five minutes, the airplane continued at the same altitude and heading with no further transmissions from the pilot. The airplane then began a descending turn to the right. Within a minute, it had descended to FL226, and its ground speed shot up from about 190 knots to 375 knots. The transponder returns were lost, but primary radar returns continued. For the next six minutes, a 6.5-mile-long cluster of primary targets was observed. The controller repeatedly tried to contact the pilot, but had no success.

The pilot held a private pilot certificate with ratings for airplane single-engine land, multi-engine land and instrument airplane. His third-class medical was current.

According to his logbook, the pilot had a total of 637.7 hours. He began flying in 2010 and received his multi-engine rating about six months before the accident. His total flight time in actual IFR was 142 hours, of which 29.8 hours were in the accident airplane. The accident airplane was equipped with a conventional panel, and a mechanic told investigators that the pilot planned to upgrade to a glass cockpit. Most of the pilot's flight time had been in a Mooney with a glass cockpit.

Records for the pressurized airplane revealed a total airframe time of 5,118.0 hours at the last annual inspection in February 2012. The right engine had 748.2 hours since overhaul, and the left engine had 755.8 hours since overhaul.

Records indicated discrepancies just before the annual inspection dealing with the autopilot, transponder and instrument system. The discrepancies were addressed with the overhaul of the encoding altimeter, rewiring of both the transponder encoding altimeter and the GPS receiver input/output data lines, and the repair of the autopilot control unit and pitch actuator. Repairs also were performed on loose hoses and fittings throughout the pitot/static system.

Satellite images showed clear skies over the route of flight.

Examination of both engines failed to reveal anything that would have prevented normal operation. Examination of various aircraft sections showed fracture features consistent with overstress separation, and no evidence of fatigue was noted. There was no evidence of bird strike, soot patterns or in-flight fire. There was no evidence consistent with control flutter.

Investigators learned that a mechanic based at a repair station at Salinas Airport was called on the morning of the accident to examine the airplane's vacuum system. He arrived at noon and spoke to the pilot who reported that the left vacuum system wasn't working for the outbound flight from Omaha, and that he suspected a vacuum line had been pinched during the avionics and autopilot maintenance work performed earlier in the week.

The mechanic found that the left vacuum pump shear coupling appeared to have failed. He tried to locate a replacement pump, but was told it would take three days to arrive in Salinas. The pilot decided not to wait around and planned to make the flight back to Omaha that night.

The Cessna 421C Information Manual states that should one of the airplane's two vacuum sources fail, "No corrective action is required by the pilot, as the system will automatically isolate the failed vacuum source, allowing normal operation on the remaining operative vacuum pump." The FAA Master Minimum Equipment List for the Cessna 421C stated that one of the vacuum pumps can be inoperative provided the airplane is operated under VFR and not operated at night. However, the regulatory basis for this Part 91 flight was such that the FAA's Minimum Equipment List requirements didn't apply.

The NTSB determined that the probable cause of this accident was the pilot's failure to regain airplane control following a sudden, rapid descent during cruise, which resulted in in-flight breakup. Contributing to the accident was the pilot's decision to make the flight with a failed vacuum pump, particularly at high altitude in night conditions.

PA-24-250
On February 20, 2012, a Piper PA-24-250 single-engine airplane crashed near Albany, Texas, killing the pilot and passenger. It was night VFR. The flight had departed Abilene, Texas, en route to Norman, Okla.

The airplane was level at 9,500 feet MSL when the pilot radioed ATC that he needed to return to Abilene because he had lost suction and his attitude indicator. Radar data showed the airplane made a climbing turn to the right and then descended rapidly. The wreckage was found the next morning. Ground and airplane impact signatures showed evidence of a nearly vertical nose-down collision with terrain. The outboard section of the right wing and the right aileron were found about one mile southeast of the main wreckage.

The private pilot had logged 502 hours with 186 hours in the PA-24-250. He had 68 hours of night experience. His third-class medical certificate was current.

At the time of the accident, the airplane had an estimated total time of 4,857.6 hours. It was equipped with an overhauled vacuum pump that had been operated for more than 12 calendar years.

A pilot operating his aircraft in the vicinity indicated that flight visibility was marginal at best, and that the area was impacted with blowing dust with an estimated in-flight visibility of one to three miles. The pilot also indicated that he could only faintly see ground lights, and at times couldn't distinguish between ground and sky.

A medical helicopter pilot operating in the area at the time of the accident reported that he was operating with his night-vision goggles due to the dark nighttime conditions, and that even with the night-vision goggles, the dust and lack of surface lights made it difficult to have any sense of horizon and made flying under visual meteorological conditions very difficult.

The vacuum pump and drive spline assembly were removed from the wreckage and examined at the NTSB Materials Laboratory in Washington, D.C. The coupler shaft was found to have fractured.

A service letter issued on March 23, 2006, by the Nichols Airborne Division, Parker Hannifin Corporation, stated that Airborne air pumps with any model number beginning with 200 through 216 must not be operated beyond the mandatory replacement time of "500 aircraft hrs. or 6 years from date of manufacture, whichever comes first." The service letter continued with the following caution: "Warning: Failure of the air pump will result in the loss of the pneumatically powered gyro flight instruments."

Another service letter, this one issued on January 21, 2007, stated that Airborne air pumps with any model number beginning with 200 through 216 must not be overhauled or repaired. The service letter continued with the following caution: "Safety Warning: Failure of an overhauled or reconditioned Parker/Airborne pneumatic component especially while flying in instrument meteorological conditions (IMC) can lead to spatial disorientation of the pilot and subsequent loss of aircraft control resulting in death, bodily injury or property damage. Overhauled or reconditioned Parker/Airborne pneumatic components must not be used and must be replaced immediately."

Yet another service letter, this one issued on February 15, 2008, stated, "All Parker/Airborne Engine Driven Air Pumps are beyond their Mandatory Replacement time and must be removed from service."

The NTSB determined that the probable cause of this accident was the loss of flight instrumentation due to a failed vacuum pump while flying at night without a discernible horizon, which resulted in the pilot's spatial disorientation and an in-flight loss of control and impact with terrain. Contributing to the accident was the continued operation of the airplane with a recalled and unsafe vacuum pump.

Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, NY 10602-0831.